The dhp1+ gene, encoding a putative nuclear 5′→3′ exoribonuclease, is required for proper chromosome segregation in fission yeast

The Schizosaccharomyces pombe dhp1(+) gene is an ortholog pf:the Saccharomyces cerevisiae RAT1 gene;,which encodes a nuclear 5'-->3' exoribonuclease, and is essential for cell viability, To clarify the:cellular functions of the nuclear 5'-->3' exoribonuclease, we isolated and characterized a temperature-sensitive mutant of dhp1(dhp1-1 mutant), The dhp1-1 mutant showed nuclear accumulation of poly(A)(+) RNA at the restrictive temperature, as was already reported for the rat1 mutant. Interestingly, the dhp1-1 mutant exhibited aberrant chromosome segregation at the restrictive temperature, The dhp1-1 cells frequently contained condensed chromosomes, most, of whose sister chromatids failed to separate during; mitosis despite normal mitotic spindle elongation, Finally, chromosomes were displaced or unequally segregated. As similar mitotic defects were also observed in Dhp1p-depleted cells, we concluded that dhp1(+) is required for proper chromosome segregation as well as for poly(A)+ RNA metabolism in fission yeast, Furthermore, we isolated a multicopy suppressor of the dhp1-1 mutant, referred to as din1(+). We found that the gene product of dhp1-1 was unstable at high temperatures, but that reduced levels of Dhp1-1p could be suppressed by overexpressing Din1p at the restrictive temperature. Thus, Din1p:may physically interact with Dhp1p and stabilize Dhp1p and/or restore its activity.